Motor neurons are neurons that control muscle function. They are located in the central nervous system and have axons that extend outside of the central nervous system in order to control muscles. Normally, upper motor neurons, which are located in the brain, transmit signals to lower motor neurons, which are located in the spinal cord, and the lower motor neurons direct muscle activity. Muscles are of course important for many activities including breathing, swallowing, talking, and walking. Therefore, damage to motor neurons or decreased motor neuron function can have devastating clinical effects, and a number of conditions associated with motor neurons have been indentified.
Such conditions include, but are not limited to, the following diseases, disorders, and injuries: amyotrophic lateral sclerosis (ALS), primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), hereditary spastic paraparesis (HSP), X-linked spinobulbar muscular atrophy (SBMA; Kenney disease), progressive bulbar palsy, pseudo-bulbar palsy, spinal muscular atrophy (SMA), post-polio syndrome (PPS), Huntington's disease, Essential tremor (ET), motor neuron disease, paralysis, and Parkinson's disease. ALS is one of the prominent of these diseases, with 1 to 2 out of 100,000 people developing ALS each year ALS is a rapidly progressive disease that is associated with the destruction of both upper and, lower motor neurons and results in the loss of voluntary muscle movement.
Some disease-modifying treatments are available for ALS and, other motor-neuron related diseases, including the use of Riluzole, which blocks certain sodium, channels that are associated with damaged neurons. While such treatments may slow disease course, there are currently no cures for motor neuron disease. Therefore, therapies that promote regeneration of the axons of motor neurons and/or promote the survival of motor neurons are of great need for patients with diseases associated with insufficient motor neuron function.